Relative navigation systems are useful for various applications such as autonomous vehicle navigation in a warehouse or factory environment, mid-air refueling, and space docking. In some applications, only the relative positions (Px, Py, Pz, or Azimuth, Elevation, Slant Range) between two objects is required. In other applications, the relative range, as well as the relative velocity (Vx, Vy, Vz, or Azimuth Rate, Elevation Rate, Slant Range Rate) and the relative attitudes (pitch, roll, and yaw) between two objects are required. Further, statistics that quantify the overall Actual Navigation Performance (ANP), in terms of Continuity, Integrity, Availability, and Accuracy (CIAA) of the relative navigation solutions, above, can be developed to allow determination of whether the ANP meets the Required Navigation Performance (RNP) for the navigation operation being conducted. In total, the relative navigation information plus the ANP statistics constitute the Navigation State Vector of the system.
In the specific case of unmanned aerial vehicles (UAVs), which are aircraft that fly without onboard pilots, relative navigation systems can be particularly useful as UAVs rely on complete or partial automation for control during their takeoff, flight, and landing. UAVs have become increasingly popular but the logistical complexity of UAV control makes their use burdensome. UAV landings are typically done at locations having traditional landing aids such as Instrument Landing Systems (ILS), Very High Frequency Omnibearing Receivers (VOR), Distance Measuring Equipment (DME) Microware Landing Systems (MLS), RADAR, etc., which aid the remote pilot, or the onboard autopilot in the case of totally autonomous systems, in landing the aircraft and/or provide for automated landings. However, it is often desirable to launch and land UAVs at locations where the infrastructure for traditional landing aids is not available, which limits the flexibility of the UAV.
With or without an onboard pilot, UAVs can be susceptible to an object intruding into the landing zone, especially temporary intrusions that occur during the act of landing. Current relative navigation systems are not able to detect such intrusions.